JPH06100714B2 - Automatic focusing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic focusing device, and more particularly to a so-called active automatic focusing device based on the principle of triangulation.

[Prior Art] One of the automatic focusing devices for a camera is a so-called active type device that measures the distance by receiving the light that is reflected by the object and returns from the light emitted from the camera toward the object. is there. In this case, the principle of triangulation is generally used as the distance measuring means. In this type of automatic focusing device, for example, when the subject is distant, or when the subject is small or its reflectance is low, the received light intensity becomes weak and accurate distance measurement cannot be performed. In this regard, a device having means for varying the gain of the light receiving element output according to the received light intensity is well known (see Japanese Patent Publication No. 55-13012). If the gain of the light-receiving element layer output is increased, the focusing operation will be performed without being affected by the distance or area of the subject or the reflectance, but on the other hand, due to the moment of inertia of the motor or the imaging lens, Since the in-focus position may be overrun, it is necessary to consider this point. Conventionally, in order to prevent the focus position from being overrun, a device has been already known in which a dead zone is provided by sandwiching the focus point and power supply to the motor is stopped when the focus position enters the dead zone. (See Japanese Patent Publication No. 56-41970).

[Problems to be Solved by the Invention] However, in the conventional device having the dead zone, the width of the dead zone is manually set and the width is set to a constant width regardless of the depth of field. The focus position is adjusted within the dead zone. In other words, when the subject is bright and the depth of field is very deep, there is no visual problem even if the focus position deviates to some extent from the in-focus point. Regardless of this, the focus is controlled so that it falls within the dead band of a certain width, so in actual useless focusing operation is performed, which not only wastes power consumption, but also results in a long focusing operation time and hunting. There were problems such as occurrence. Note that there is known a device in which the focusing accuracy is changed in conjunction with the aperture in order to change the focusing accuracy according to the depth of field. There was a problem that the zoom lens and other interchangeable lenses could not be used because the depth of field changes depending on the distance.

On the other hand, although a method of setting the dead zone based on the contrast information obtained as the output of the line sensor itself as a distance measuring element has been proposed, the method of obtaining the contrast information by the line sensor is not affected by disturbances such as camera shake. There is a problem that it is weak and it is difficult to realize stable control.

The present invention is made in view of such a problem, and the accuracy of focus determination is set appropriately according to the depth of field, and unnecessary high-precision focus adjustment operation is performed. It is an object of the present invention to provide an automatic focusing device that is not performed.

[Means and Actions for Solving Problems] This automatic focusing device includes an image pickup means for generating a video signal corresponding to an image of a subject by an optical member, and a light projecting means for projecting a light beam toward the subject. And a light receiving means for receiving the reflected light of the light beam from the subject and a focus determination operation based on an output signal of the light receiving means to generate an adjustment signal for focus adjustment. In the automatic focusing device, the dead zone relating to the determination operation is variably set based on the setting information supplied from the other means, wherein the adjusting means outputs the output of the image pickup means. It is configured such that the dead zone is variably set based on the setting information corresponding to the output of the high frequency component extraction means provided to extract the high frequency component from Listen Indeed waste due to the width of the dead zone is excessively to maintain the focusing accuracy high standard wider is eliminated.

[Embodiment] Hereinafter, the present invention will be described based on an illustrated embodiment.

FIG. 1 is a block diagram of an electric circuit of an automatic focusing device in a video camera, an electronic still camera or the like showing an embodiment of the present invention. In FIG. 1, a light beam such as infrared light as the distance detection light projected by the light projection means 1 is applied to the subject 2, and its reflected light is reflected by the light receiving means 3
The light enters the first and second light receiving portions 3a and 3b. The signals photoelectrically converted by the light receiving portions 3a and 3b are guided to the first and second variable gain amplifiers 4a and 4b so that the sum of both outputs becomes constant in these variable gain amplifiers 4a and 4b. Level controlled. That is, when the outputs of the variable gain amplifiers 4a and 4b are guided to the gain setting signal generation circuit 5, for example, the distance of the subject 2 is long, the reflectance of the subject 2 is low, and the variable gain amplifiers are low.
When the output levels of 4a and 4b are low, the gain setting signal generating circuit 5 generates a gain setting signal that changes according to the sum of the outputs of the variable gain amplifiers 4a and 4b, and increases the gains of the variable gain amplifiers 4a and 4b. To be controlled. In this way, the outputs of the variable gain amplifiers 4a and 4b are output by the gain setting signal generating circuit 5.
Feedback is applied so that it does not change depending on the reflectance or distance of the subject 2.

The outputs of the variable gain amplifiers 4a and 4b are guided to the adjusting circuit 6, and the adjusting circuit 6 detects the polarity and magnitude of the difference signal between the two outputs. That is, there is a level difference between the photoelectric conversion outputs of the first and second light receiving portions 3a and 3b depending on the position of the subject 2, so that whichever of the outputs of the variable gain amplifiers 4a and 4b is larger is in the front focus state. The adjustment circuit 6 detects the amount of deviation from the in-focus point depending on whether there is a rear focus state or whether there is a rear focus state or the magnitude of the output difference between the variable gain amplifiers 4a and 4b.
An automatic focus adjustment signal is detected from the adjustment circuit 6. This automatic focus adjustment signal is used as a focus control signal for a motor that drives the imaging lens 7 to a focus position.

On the other hand, the optical image of the subject 2 is taken by the image pickup lens 7 to the image pickup tube 8
An image is formed on the image pickup surface of, and is converted into a video signal by the image pickup tube 8. The high frequency component of the video signal obtained by the image pickup tube 8 is detected by the high frequency component detection circuit 9 and is adjusted by the adjustment circuit 6.
Is input as a control signal of the dead zone setting circuit configured in the same circuit. The control signal of the high frequency component controls the focus dead zone of the output difference signal of the variable gain amplifiers 4a and 4b guided to the adjusting circuit 6 according to the level of the high frequency component, and the adjusting circuit 6 automatically adjusts the focus. The control signal is output.

Next, the operation of the apparatus of the above embodiment will be described.

When the light beam from the light projecting means 1 is reflected by the subject 2 and enters the light receiving means 3, the light receiving portions 3a and 3b output photoelectric conversion signals corresponding to the respective amounts of incident light, and the variable gain amplifiers 4a and 4b.
As described above, the gain setting signal generating circuit 5 removes the influence of the reflectance and the distance of the subject 2 that appear as the fluctuation of the sum of the photoelectric conversion signals, and the variable gain amplifiers 4a, 4a
Focus state information based on the output difference of b is input to the adjustment circuit 6.

Here, assuming that the focus position of the subject 2 by the imaging lens 7 is deviated from the in-focus point in a certain direction, the automatic focus adjustment signal is a variable gain amplifier 4 based on the amount of deviation from the in-focus point.
The drive motor of the image pickup lens 7 is controlled according to the output difference between a and 4b, and the focus position changes in the direction approaching the in-focus point as shown by the solid line f in FIG. By the way, the level of the control signal composed of the high-frequency component, which is the output of the high-frequency component detection circuit 9, is lower as the amount of deviation from the in-focus point is larger, that is, the degree of blurring is larger. Since this control signal controls the width of the focus dead zone in the adjusting circuit 6, for example, as shown in FIG. 2, at the initial time point t ₀ where the shift amount of the focus position is the largest,
The width of the dead zone between the in-focus point and the position indicated by the broken line g is narrow, and the in-focus operation is started by the automatic focus adjustment signal. When the shift amount is gradually reduced by performing the focusing operation, the captured image becomes clearer, the high-frequency component of the video signal increases, and the control signal increases. The width gradually becomes wider with the focusing operation.
The amount of deviation shown by the solid line f gradually decreases, and the focus position becomes
When entering the gradually increasing dead zone, at this time point t ₁ , the autofocus signal stops driving the motor and stops the focusing operation. Then, thereafter, the imaging lens 7 further moves toward the in-focus point by the moment of inertia of the lens and the motor, and then stops. At this time, the imaging lens 7 does not always stop at the in-focus point, and the difference d between the in-focus position and the in-focus point at this time is the in-focus accuracy.

Here, considering the case where the aperture is narrowed down to some extent and the depth of field becomes deep, even if the amount of shift of the focus position is the same and changes as shown by the solid line f in FIG. Since the high frequency component of the video signal becomes larger than that when the depth of field is shallow, the dead band is further widened by the control signal from the high frequency component detection circuit 9 as shown by the chain line g'in FIG. While the amount of deviation from the focus is large, the focusing operation ends at time t ₁ ′. Therefore,
In this case, the imaging lens 7 stops at the focal position indicated by the chain double-dashed line f'due to the moment of inertia, and the focusing accuracy at this time becomes d ', so that the focusing accuracy is higher than that when the depth of field is shallow. However, as long as the focus position is within the dead zone as described above, a clear image with no blurring can be visually obtained. As described above, since the focus dead zone is controlled by the magnitude of the high frequency component included in the video signal, an unnecessary focus operation is not performed, and thus a quick focus operation can be performed. It is possible to save power consumption. In addition, since the dead zone is wide during focusing, even if there is noise or slight movement of the subject that does not need to follow the focusing operation, these are areas that are considered to be in focus (dead zone).
This will cause internal fluctuations and prevent hunting. And
Even if the focal length changes by using another interchangeable lens or zoom lens, the above-mentioned operation does not change and the effect is the same.

FIG. 3 is a block diagram of an electric circuit of an automatic focusing device showing another embodiment of the present invention. In the apparatus of the embodiment shown in FIG. 3, a high-pass filter (hereinafter, referred to as HPF) 10, in place of the high-frequency component detection circuit 9 (see FIG. 1) used in the embodiment, is provided at the subsequent stage of the image pickup tube 8. Automatic gain control circuit (hereinafter referred to as AGC) 11, bandpass filter (hereinafter referred to as BP
F) 12a, 12b and a decision signal generation circuit 13 are provided. The high frequency component contained in the video signal output from the image pickup tube 8 is detected by the HPF 10 and then made to have a constant level by the AGC 11, and then guided to the BPF 12a and BPF 12b to detect two high frequency signals having slightly different frequencies. This 2
When the two high frequency signals are input to the determination signal generation circuit 13,
The determination signal generating circuit 13 obtains the difference between the two high frequency signals, and the resolution limit frequency S ₁ is calculated from the magnitude of the difference signal and the two frequencies. Then, the determination signal that changes depending on the resolution limit frequency S ₁ is the adjustment circuit 6
It is input as a control signal for variably setting the dead zone to the dead zone setting circuit therein.

Here, the resolution limit frequency S ₁ will be described. FIG. 4 is a diagram showing contrast, and the pattern of the diagram shows the degree of focusing. The dotted line indicates OTF (Optical Transformer Function). Further, in FIG. 4, it is shown that the determination signal generating circuit 13 detects the difference C between the signal levels at the frequency positions A and B in the signal pass band of the BPFs 12a and 12b. Here, in FIG. 4, the resolution limit frequency S ₁ close to the frequency positions A and B is the radius of the circle of confusion (blurring circle) b
Then, S ₁ = 0.61 / b, and the position of the resolution limit frequency S ₁ moves due to the radius b of the circle of confusion. If an image is formed by a lens having such a spatial frequency distribution, the spatial frequency distribution H of the image
(Ω) is represented by H (ω) = F (ω) · G (ω) by the spatial frequency distribution F (ω) of the subject and the spatial frequency distribution G (ω) of the lens. In a general subject, the spatial frequency distribution shows a gradual change. Therefore, the spatial frequency distribution H of the image
(Ω) shows almost the same inclination as the spatial frequency distribution G (ω) of the lens. In the spatial frequency distribution G (ω) of the lens, the slope does not change much depending on the frequency near the resolution limit frequency S ₁ and becomes a substantially straight line. Therefore, as shown in FIG. 4, in the present embodiment, the levels of two frequency positions A and B which are near the resolution limit frequency S ₁ and are not in the false resolution region I and are extremely slightly apart are set. The position of the resolution limit frequency S ₁ can be estimated by measuring the difference C and the frequency positions A and B to obtain the slope of the frequency distribution characteristic shown in FIG.

Therefore, when the focus is defocused, the higher frequency level of the high frequency component of the video signal is lower than that at the time of focusing, and the output of the BPF 12b on the high frequency side, that is, the frequency position B in FIG. Therefore, the level difference C becomes large, the slope of the frequency distribution becomes steep, and the position of the resolution limit frequency S ₁ goes down. This controls the determination signal generated from the determination signal generation circuit 13 so that the width of the dead zone is set narrow in the adjustment circuit 6. For this reason,
The image pickup lens 7 is operated by the automatic focusing signal from the adjusting circuit 6.
The drive motor of is controlled toward the focal point. Then, when the focus comes into focus, the output of the BPF 12b rises, the level difference C becomes small, and the inclination of the frequency distribution becomes gentle. Therefore, the position of the resolution limit frequency S ₁ rises, and with this, The dead band is gradually widened. Then, the focusing operation is stopped when the focus position enters the focusing dead zone.

According to this embodiment, the best focus state can be obtained without being affected by the spatial frequency of the subject. Therefore, it is also effective for a subject with low contrast.

FIG. 5 is a block diagram of an electric circuit of an automatic focusing device showing still another embodiment of the present invention. In the embodiment apparatus shown in FIG. 5, buffer amplifiers 14a, 14b are used instead of the variable gain amplifiers 4a, 4b in the embodiment apparatus shown in FIG.
And outputs the outputs of the buffer amplifiers 14a and 14b to the summing amplifier 15
And the sum is added, and the gain of the variable gain amplifier 16 is changed by the added output. The variable gain amplifier 16 amplifies the judgment signal output from the judgment signal generating circuit 13 in correspondence with the resolution limit frequency S ₁ and guides it to the dead zone setting circuit of the adjusting circuit 6. Therefore, in this embodiment, when the amount of incident light is large and the output of the summing amplifier 15 increases, the level of the determination signal guided from the determination signal generation circuit 16 to the adjustment circuit 6 increases and the dead band is widened.

[Advantages of the Invention] As described above, according to the present invention, the focus dead zone is controlled by the high frequency component included in the output of the image pickup means, and the accuracy of the focus determination is the depth of field. The focus adjustment operation is not performed unnecessarily with high accuracy, so focus operation is performed in a short time, power consumption is saved, and noise is hypersensitive. It is possible to effectively avoid a reaction or excessive wear of the movable part.

In addition, since the dead zone is set based on the output of the image pickup device that performs photoelectric conversion of a two-dimensional optical image, this setting is made based on the contrast information from a far wider field of view than a line sensor or the like. As a result, stable control is realized, which is strong against external disturbances caused by movement such as camera shake. Furthermore, since the construction is simple and the control algorithm can be simplified, the development cost of the practical system is suppressed, and therefore, an inexpensive and practical automatic focusing device of this type can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric circuit of an automatic focusing device showing an embodiment of the present invention, and FIG. 2 is a diagram for explaining a focusing operation by the automatic focusing device shown in FIG. FIG. 3 is a block diagram of an electric circuit of an automatic focusing device showing another embodiment of the present invention, and FIG. 4 is a contrast line for explaining the operation of the automatic focusing device shown in FIG. FIG. 5 is a block diagram of an electric circuit of an automatic focusing device showing still another embodiment of the present invention. 1 ... Light projecting means 3 ... Light receiving means 6 ... Adjusting circuit 7 ... Imaging lens (optical system) 8 ... Imaging tube (imaging means) 9 ... High frequency component detection circuit (high frequency component extraction circuit) 10 ... HPF (high frequency component extraction circuit) 11 …… AGC (high frequency component extraction circuit) 12a, 12b …… BPF (high frequency component extraction circuit) 13 …… decision signal generation circuit (high frequency component extraction circuit)

Claims (1)

[Claims] 1. An image pickup means for generating a video signal corresponding to an image of a subject by an optical system, a light projecting means for projecting a light beam toward the subject, and light reflected by the subject for the light beam. Regarding the light receiving means and the focus determination operation based on the triangulation principle based on the output signal of the light receiving means to generate the adjustment signal for the focus adjustment, the dead zone related to this focus determination operation is the other. Adjusting means adapted to be variably set based on the setting information supplied from the adjusting means, wherein the adjusting means extracts a high frequency component from the output of the image pickup means. An automatic focusing device characterized in that the dead zone is variably set based on setting information corresponding to the output of the high-frequency component extracting means provided in.